#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main() {
	int n;
	int arr[55] = { 0,0,1,1 };
	scanf("%d", &n);
	for (int i = 4; i <= n; i++) {
		arr[i] = arr[i - 2] + arr[i - 3];
	}
	printf("%d", arr[n]);
	return 0;
}